(1) Field of the Invention
This invention relates to a process for the production of acetaldehyde and ethanol by reacting methanol with hydrogen and carbon monoxide in the presence of a catalyst system which, in addition to cobalt, contains a metal from the group comprising chromium, molybdenum, tungsten, titanium, vanadium, iron, nickel, as well as halogen as promoter and a polydentate ligand.
(2) Description of the Prior Art
Acetaldehyde and ethanol are important organic starting materials. It is known that they can be obtained by the homologisation of methanol. To this end, methanol is reacted with hydrogen and carbonmonoxide at elevated temperature and pressure in the presence of a catalyst system of cobalt, a halogen, preferably iodine, as promoter and a ligand, for example a tertiary monophosphine, the reaction optionally being carried out in a solvent (EPA No. 0,001,937). Methanol conversions of up to 57.7% are obtained for an ethanol selectivity, including the secondary products which can be worked up into ethanol, of 55.8%, in other words the yield of ethanol amounts to 32.2%, based on the methanol used. Recently the mono-ligand has been replaced by so-called polydentate ligands, e.g. ligands containing 2 or more central atoms, for example phosphorus (EPA No. 0,010,373). In this case, too, the reaction is carried out at elevated temperature (150.degree.-250.degree. C.) and pressure (100-300 bars). Synthesis gas obtained by gasifying coal for example is used as the gas containing hydrogen and carbon monoxide. In the absence of a solvent, the yield of ethanol amounts to 32.9% and, in the presence of a solvent, to 36.3%. In this connection, it has also been proposed to introduce a second metal, namely ruthenium, into the catalyst system. This is in line with earlier proposals to add a noble metal, namely ruthenium or osmium, during the homologisation of methanol activated by cobalt, halogen and a monophosphine ligand (U.S. Pat. No. 4,133,966).
Although it has been possible to increase the conversion and selectivity of the homologisation reactions by virtue of the improvements made in recent years to the catalysts used, a further increase in these values is still desirable.